Microorganisms do not exist individually but are part of dynamic polymicrobial communities. Humans harbor polymicrobial communities that form biofilms in close proximity to different epithelial surfaces. In the oral cavity, biofilms mostly form on teeth or prosthetic devices and adjacent to the oral mucosa. In the susceptible host, oral biofilms containing species such as Candida albicans or Porphyromonas gingivalis constitute the primary etiology of infectious and inflammatory conditions such as candidiasis and periodontal disease. Therefore, the identification of strategies to eradicate oral biofilms or interfere with their development will aid in the treatment or prevention of such conditions. In order to develop such strategies we need to understand the factors that govern the formation of oral polymicrobial biofilm communities, including both the interactions occurring among community members and the role of the host in shaping biofilm characteristics. In this pilot grant we will characterize a novel in vitro model system where such questions can begin to be answered. The proposed model consists of a flow cell device designed to harbor a polymicrobial biofilm growing in the presence of an oral mucosa tissue analogue. In Aim A we will characterize the biofilm component of our model by determining the optimal experimental conditions for polymicrobial biofilm assembly by microbial consortia containing an oral pathogen (either P. gingivalis or C. albicans). In Aim B we will characterize the tissue component of our model (an oral mucosa 3-D analogue) by evaluating the production of cytokines and anti-microbial peptides in the presence and absence of biofilms under flow conditions. Finally, in Aim C we will examine the role of the adjacent epithelium on polymicrobial biofilm assembly and identify, via microarrays, genes differentially regulated by the host in C. albicans and P. gingivalis when forming part of a polymicrobial community. We envision that our new model will lead to the discovery of host factors that influence biofilm development in the oral environment. Such host factors can be examined further to understand their role in shaping polymicrobial biofilm growth in the oral cavity and oral biofilm-related disease susceptibility traits in humans. Furthermore, a better understanding of polymicrobial biofilm-host interactions will lead to the development of novel therapeutic strategies to interfere with biofilm formation.